diff --git a/.github/workflows/on_commit.yml b/.github/workflows/on_commit.yml
new file mode 100644
index 0000000..2786694
--- /dev/null
+++ b/.github/workflows/on_commit.yml
@@ -0,0 +1,29 @@
+---
+name: CI
+
+on:
+  workflow_dispatch:
+
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: 🛎️ Checkout
+        uses: actions/checkout@v4
+
+      - name: ⚙️ Setup Bun
+        uses: oven-sh/setup-bun@v1
+
+      - name: 📦 Build
+        env:
+          NODE_ENV: production
+          FORCE_COLOR: 1
+        run: |
+          bun install
+          make --output-sync --jobs fmt test
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..940b884
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+node_modules/
+**/*.mmdb
+lib/**/*.d.*ts
+lib/**/index.mjs
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..55aa560
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,20 @@
+.PHONY : all test
+all :
+
+.PHONY : lib/maxmind
+lib/maxmind :
+	@ $(MAKE) --directory=lib/maxmind
+
+.PHONY : fmt
+fmt :
+	bun x prettier --write .
+	@ git diff-index --quiet HEAD
+
+.PHONY : test
+test :
+	@ $(MAKE) --directory=lib/maxmind test
+
+.PHONY : distclean
+distclean :
+	-rm -r node_modules
+	-@ $(MAKE) --directory=lib/maxmind clean
diff --git a/lib/maxmind/Makefile b/lib/maxmind/Makefile
new file mode 100644
index 0000000..692c0b6
--- /dev/null
+++ b/lib/maxmind/Makefile
@@ -0,0 +1,16 @@
+.PHONY : all test clean
+all : test/GeoLite2-Country-Test.mmdb index.mjs
+
+index.mjs : index.mts
+	bun x tsc --pretty
+	bun x webpack
+
+test/GeoLite2-Country-Test.mmdb :
+	cd test && wget 'https://cdn.jsdelivr.net/gh/maxmind/MaxMind-DB/test-data/GeoLite2-Country-Test.mmdb'
+
+test :
+	cd test && bun x tsc
+	cd test && bun test
+
+clean :
+	- rm test/*.mmdb *.d.mts index.*js
diff --git a/lib/maxmind/index.mts b/lib/maxmind/index.mts
new file mode 100644
index 0000000..9d5de03
--- /dev/null
+++ b/lib/maxmind/index.mts
@@ -0,0 +1,8 @@
+import type { CountryResponse } from 'mmdb-lib';
+import { Reader } from 'mmdb-lib';
+
+export async function init(response: Pick<Response, 'arrayBuffer'>) {
+  const db = Buffer.from(await response.arrayBuffer());
+
+  return new Reader<CountryResponse>(db);
+}
diff --git a/lib/maxmind/test/maxmind.spec.ts b/lib/maxmind/test/maxmind.spec.ts
new file mode 100644
index 0000000..f9dc531
--- /dev/null
+++ b/lib/maxmind/test/maxmind.spec.ts
@@ -0,0 +1,210 @@
+import { describe, expect, it } from 'bun:test';
+import fs from 'node:fs/promises';
+import { fileURLToPath } from 'node:url';
+
+import * as maxmind from '../index.mjs';
+
+describe('lib / maxmind', () => {
+  const arrayBuffer = fs
+    .readFile(
+      fileURLToPath(import.meta.resolve('./GeoLite2-Country-Test.mmdb')),
+    )
+    .then(({ buffer }) => buffer as ArrayBuffer);
+  const mockDatabase = { arrayBuffer: () => arrayBuffer };
+
+  it('should resolve a country for IPv4', async () => {
+    const reader = await maxmind.init(mockDatabase);
+
+    expect(reader.get('89.160.20.122')).toStrictEqual({
+      continent: {
+        code: 'EU',
+        geoname_id: 6255148,
+        names: {
+          de: 'Europa',
+          en: 'Europe',
+          es: 'Europa',
+          fr: 'Europe',
+          ja: 'ヨーロッパ',
+          'pt-BR': 'Europa',
+          ru: 'Европа',
+          'zh-CN': '欧洲',
+        },
+      },
+      country: {
+        geoname_id: 2661886,
+        is_in_european_union: true,
+        iso_code: 'SE',
+        names: {
+          de: 'Schweden',
+          en: 'Sweden',
+          es: 'Suecia',
+          fr: 'Suède',
+          ja: 'スウェーデン王国',
+          'pt-BR': 'Suécia',
+          ru: 'Швеция',
+          'zh-CN': '瑞典',
+        },
+      },
+      registered_country: {
+        geoname_id: 2921044,
+        is_in_european_union: true,
+        iso_code: 'DE',
+        names: {
+          de: 'Deutschland',
+          en: 'Germany',
+          es: 'Alemania',
+          fr: 'Allemagne',
+          ja: 'ドイツ連邦共和国',
+          'pt-BR': 'Alemanha',
+          ru: 'Германия',
+          'zh-CN': '德国',
+        },
+      },
+    });
+
+    expect(reader.get('67.43.156.156')).toStrictEqual({
+      continent: {
+        code: 'AS',
+        geoname_id: 6255147,
+        names: {
+          de: 'Asien',
+          en: 'Asia',
+          es: 'Asia',
+          fr: 'Asie',
+          ja: 'アジア',
+          'pt-BR': 'Ásia',
+          ru: 'Азия',
+          'zh-CN': '亚洲',
+        },
+      },
+      country: {
+        geoname_id: 1252634,
+        iso_code: 'BT',
+        names: {
+          de: 'Bhutan',
+          en: 'Bhutan',
+          es: 'Bután',
+          fr: 'Bhutan',
+          ja: 'ブータン王国',
+          'pt-BR': 'Butão',
+          ru: 'Бутан',
+          'zh-CN': '不丹',
+        },
+      },
+      registered_country: {
+        geoname_id: 798549,
+        is_in_european_union: true,
+        iso_code: 'RO',
+        names: {
+          de: 'Rumänien',
+          en: 'Romania',
+          es: 'Rumanía',
+          fr: 'Roumanie',
+          ja: 'ルーマニア',
+          'pt-BR': 'Romênia',
+          ru: 'Румыния',
+          'zh-CN': '罗马尼亚',
+        },
+      },
+      traits: {
+        is_anonymous_proxy: true,
+      },
+    });
+  });
+
+  it('should resolve a country for IPv6', async () => {
+    const reader = await maxmind.init(mockDatabase);
+
+    expect(reader.get('2a02:fc40::1')).toStrictEqual({
+      continent: {
+        code: 'EU',
+        geoname_id: 6255148,
+        names: {
+          de: 'Europa',
+          en: 'Europe',
+          es: 'Europa',
+          fr: 'Europe',
+          ja: 'ヨーロッパ',
+          'pt-BR': 'Europa',
+          ru: 'Европа',
+          'zh-CN': '欧洲',
+        },
+      },
+      country: {
+        geoname_id: 2623032,
+        is_in_european_union: true,
+        iso_code: 'DK',
+        names: {
+          de: 'Dänemark',
+          en: 'Denmark',
+          es: 'Dinamarca',
+          fr: 'Danemark',
+          ja: 'デンマーク王国',
+          'pt-BR': 'Dinamarca',
+          ru: 'Дания',
+          'zh-CN': '丹麦',
+        },
+      },
+      registered_country: {
+        geoname_id: 2623032,
+        is_in_european_union: true,
+        iso_code: 'DK',
+        names: {
+          de: 'Dänemark',
+          en: 'Denmark',
+          es: 'Dinamarca',
+          fr: 'Danemark',
+          ja: 'デンマーク王国',
+          'pt-BR': 'Dinamarca',
+          ru: 'Дания',
+          'zh-CN': '丹麦',
+        },
+      },
+    });
+
+    expect(reader.get('2a02:d300::1')).toStrictEqual({
+      continent: {
+        code: 'EU',
+        geoname_id: 6255148,
+        names: {
+          de: 'Europa',
+          en: 'Europe',
+          es: 'Europa',
+          fr: 'Europe',
+          ja: 'ヨーロッパ',
+          'pt-BR': 'Europa',
+          ru: 'Европа',
+          'zh-CN': '欧洲',
+        },
+      },
+      country: {
+        geoname_id: 690791,
+        iso_code: 'UA',
+        names: {
+          de: 'Ukraine',
+          en: 'Ukraine',
+          es: 'Ucrania',
+          fr: 'Ukraine',
+          ja: 'ウクライナ共和国',
+          'pt-BR': 'Ucrânia',
+          ru: 'Украина',
+          'zh-CN': '乌克兰',
+        },
+      },
+      registered_country: {
+        geoname_id: 690791,
+        iso_code: 'UA',
+        names: {
+          de: 'Ukraine',
+          en: 'Ukraine',
+          es: 'Ucrania',
+          fr: 'Ukraine',
+          ja: 'ウクライナ共和国',
+          'pt-BR': 'Ucrânia',
+          ru: 'Украина',
+          'zh-CN': '乌克兰',
+        },
+      },
+    });
+  });
+});
diff --git a/lib/maxmind/test/tsconfig.json b/lib/maxmind/test/tsconfig.json
new file mode 100644
index 0000000..e1b4cde
--- /dev/null
+++ b/lib/maxmind/test/tsconfig.json
@@ -0,0 +1,15 @@
+{
+  "$schema": "https://json.schemastore.org/tsconfig",
+
+  "include": ["*.ts"],
+
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "Preserve",
+    "skipLibCheck": true,
+    "noEmit": true,
+
+    "strict": true,
+    "forceConsistentCasingInFileNames": true
+  }
+}
diff --git a/lib/maxmind/tsconfig.json b/lib/maxmind/tsconfig.json
new file mode 100644
index 0000000..03b1762
--- /dev/null
+++ b/lib/maxmind/tsconfig.json
@@ -0,0 +1,15 @@
+{
+  "$schema": "https://json.schemastore.org/tsconfig",
+
+  "include": ["*.mts", "webpack.config.mjs"],
+
+  "compilerOptions": {
+    "target": "ESNext",
+    "module": "Preserve",
+    "types": [],
+    "declaration": true,
+
+    "strict": true,
+    "forceConsistentCasingInFileNames": true
+  }
+}
diff --git a/lib/maxmind/webpack.config.mjs b/lib/maxmind/webpack.config.mjs
new file mode 100644
index 0000000..54625d8
--- /dev/null
+++ b/lib/maxmind/webpack.config.mjs
@@ -0,0 +1,30 @@
+// @ts-check
+
+import { fileURLToPath } from 'node:url';
+
+import webpack from 'webpack';
+
+/** @type webpack.Configuration */
+const config = {
+  mode: 'none',
+  experiments: { outputModule: true },
+
+  entry: { index: fileURLToPath(import.meta.resolve('./index.mjs')) },
+  output: {
+    path: fileURLToPath(import.meta.resolve('.')),
+    libraryTarget: 'module',
+  },
+
+  resolve: {
+    fallback: {
+      net: false,
+    },
+  },
+  plugins: [
+    new webpack.ProvidePlugin({
+      Buffer: ['buffer', 'Buffer'],
+    }),
+  ],
+};
+
+export default config;
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..e1f8d11
--- /dev/null
+++ b/package.json
@@ -0,0 +1,26 @@
+{
+  "private": true,
+  "name": "ctf",
+  "version": "0.1.0",
+  "author": "nilfalse.com",
+  "license": "MPL-2.0",
+  "type": "module",
+  "scripts": {
+    "postinstall": "make lib/maxmind"
+  },
+  "dependencies": {
+    "buffer": "^6.0.3",
+    "mmdb-lib": "^2.1.1"
+  },
+  "devDependencies": {
+    "@types/bun": "latest",
+    "prettier": "^3.3.1",
+    "webpack-cli": "^5.1.4"
+  },
+  "peerDependencies": {
+    "typescript": "*"
+  },
+  "prettier": {
+    "singleQuote": true
+  }
+}